Ground Cover South : Ground Cover 056 June-July 2005 - South
At the end of the day it seems clear that the long-term practice of no-till conservation farming brings benefits to soil environment on which we rely for world food production. In doing so it allows farmers to produce higher amounts of a better quality product with lower inorganic inputs such as nitrogen fertiliser. For more information: Tristan Baldock, 08 8682 2755, email@example.com Footnote: This research is supported by the South Australian No Till Farmers Association, GRDC and the University of Adelaide. n World population growth dictates that world food production must increase significantly, and with this it becomes increasingly important to reduce inputs and increase the outputs of farming systems, in an environmentally sustainable way. No-till farming systems have been researched and practised for many decades, but the adoption of this conservation farming practice has only been significant in Australia over the past 10 to 20 years. And while there have been many studies on no-till, some of which present conflicting evidence, there has been little work done on the long-term effects -- particularly in terms of soil nitrogen supply and subsequent grain yield and protein levels. In 2004, field trials at Lock on the Eyre Peninsula and at Hart in the mid- north of South Australia examined the effect of 15 years of no-till on soil nitrogen, yield and protein. The trials also examined the effect of five different rates of nitrogen fertiliser (urea) applied to each tillage treatment at the time of sowing (using deep banding), to see if changes in soil nitrogen supply under no- till could reduce fertiliser requirements. The overarching objective was to see what effect long-term no-till has on the yield and protein content of spring wheat in low and medium rainfall zones. At each of the trial locations, two contrasting sites were selected, one meeting the criterion of long-term no- till with stubble retention, the other a conventional system going into its first year of no-till. These two contrasting paddocks were close enough to minimise variation in precipitation and soil type. The Hart site was sown with blanket treatments of 100 kilograms per hectare of granular 18:20, whereas Lock had a blanket treatment of 58 litres per hectare of liquid fertiliser (N8:P12:Zn0.7:Cu0.4:Mn1.2kg). SOIL CARBON AND NITROGEN Pre-sowing soil tests, to a depth of 60 centimetres in 20cm increments, show that long-term no-till at Lock had significantly more carbon throughout the soil profile, particularly at 20 to 40cm. This suggests there is some change in the chemical and physical properties of the soil due to no-till, allowing carbon to penetrate deeper into the profile. At Hart, the finer textured soils, which naturally have higher organic levels protected by clay particles, made the same differences harder to detect. While it is known that stubble residue takes longer to decompose if not incorporated by tillage, this is more than compensated for over time. After several years this stubble layer stimulates the development of soil fauna and increased microbial activity. Evidence of this is seen in the measures of microbial biomass. Long-term no-till has clearly had a positive effect on the Lock soils with increased microbial biomass in the top soil and at 40 to 60cm. This said, a definitive trend cannot be drawn from the trials for reasons explained in Figure 1. AVAILABLE NITROGEN The measure of available nitrogen is important because it represents the potential plant nitrogen uptake. At Lock the long-term treatment showed significantly higher levels of available nitrogen and it would appear that soil is playing a significant role in supplying available nitrogen to the plant. If this is the case, it lowers the need for nitrogen fertiliser. However, the results were not as supportive of this hypothesis at Hart, where available soil nitrogen concentrations were higher under the short-term treatment in April -- but also higher in the top 20cm under long-term treatment in August. These results may be due to a recent rotation of oaten hay (which tends to drain the soil of available nitrogen) in the long-term area, while the short-term site had been sown to canola in 2003. Canola is thought to increase available nitrogen through 'biofumigation'. As for actual nitrogen uptake, this was significantly higher at both Lock and Hart on the long-term no-till sites. This is attributed to improved root growth through better soil condition from long-term reduced tillage, and the increased availability and mineralisation of nitrogen through long-term stubble retention. In the measurement of herbage nitrogen at anthesis (flowering) the short-term no-till plants had lower nitrogen content -- even after fertiliser applications as high as 80kg of nitrogen. This suggests the soil (rather than the applied fertiliser) is supplying greater amounts of available nitrogen to the plants under long-term no-till. DRY MATTER YIELD The final yield of grain or dry matter is the ultimate measure of the effectiveness of an agronomic practice in improving production. In this experiment, dry matter yields were taken at anthesis (GS 6.1) as the definitive comparison between long- term and short-term no-tillage treatments. Dry matter yield at anthesis is a reasonably good indicator of the final grain yield of that crop, unless water suddenly becomes very limiting -- which is what happened at Lock. NO-TILL POINTS TO NITROGEN RETHINK Some of the first long-term studies into the effects of no-till are pointing to the need for further research on how it influences nitrogen management, reports Tristan Baldock Tristan Baldock explaining the results of his no-till trials at the Adelaide grains research updates. PHOTO: BRAD COLLIS No-till 13 JUNE/JULY 2005 GROUND COVER At Hart, long-term no-till consistently yielded significantly more dry matter in all nitrogen treatments. And short-term no-till, even after the application of 80kg of nitrogen fertiliser, still yielded significantly less than long-term no-till with zero nitrogen fertiliser. IMPLICATIONS This research has only been carried out for one season, and needs to be validated by continued trials. However it is in line with the results from similar trials in Canada. If these preliminary results do hold true in future years, it is going to mean changes in fertiliser application rates, and possibly changes in timing and methods of nitrogen application as well. KEY POINTS: n Long-term no-till appears to create a better 'flow' of available nitrogen, with increased nitrogen available to the plant throughout the season. n Long-term no-till management increases total carbon and nitrogen, and microbial biomass. n Increased duration of no-till management needs less added nitrogen fertiliser to achieve similar growth responses. n Higher grain yields and grain nitrogen contents are achievable with lower N inputs under long-term no-till. Hart 0-20cm Hart 20-40cm Hart 40-60cm Lock 0-20cm Lock 20-40cm Lock 40-60cm Tillage treatment Short term Long term (Hart) (Lock) (Hart) (Lock) 70 80 50 60 30 40 20 10 0 Figure 1. Microbial biomass at various depths Carbon kg/ha The graph shows no clear trends because the Hart site showed higher levels of microbial nitrogen and carbon under the short-term history, while the reverse was true at Lock. Microbial activity was greater in the top 10cm of soil under short-term, possibly due to frequent cultivation acting as a stimulant. Long-term no-till has had a positive effect on the Lock soils with an increased microbial biomass in the top soil and at 40 to 60cm, although the same conclusions are not as clear at Hart, possibly due to a lower pH and less calcium.
Ground Cover 057 August-September 2005 - South
Ground Cover 055 April-May 2005 - South